Problem: Nauuo is a girl who loves playing chess.

One day she invented a game by herself which needs n chess pieces to play on a m× m chessboard. The rows and columns are numbered from 1 to m. We denote a cell on the intersection of the r-th row and c-th column as (r,c).

The game's goal is to place n chess pieces numbered from 1 to n on the chessboard, the i-th piece lies on (r_i,\,c_i), while the following rule is satisfied: for all pairs of pieces i and j, |r_i-r_j|+|c_i-c_j|≥|i-j|. Here |x| means the absolute value of x.

However, Nauuo discovered that sometimes she couldn't find a solution because the chessboard was too small.

She wants to find the smallest chessboard on which she can put n pieces according to the rules.

She also wonders how to place the pieces on such a chessboard. Can you help her?

Input

The only line contains a single integer n (1≤ n≤ 1000) — the number of chess pieces for the game.

Output

The first line contains a single integer — the minimum value of m, where m is the length of sides of the suitable chessboard.

The i-th of the next n lines contains two integers r_i and c_i (1≤ r_i,c_i≤ m) — the coordinates of the i-th chess piece.

If there are multiple answers, print any.

Examples

Input


2


Output


2
1 1
1 2

Input


4


Output


3
1 1
1 3
3 1
3 3

Note

In the first example, you can't place the two pieces on a 1×1 chessboard without breaking the rule. But you can place two pieces on a 2×2 chessboard like this:

<image>

In the second example, you can't place four pieces on a 2×2 chessboard without breaking the rule. For example, if you place the pieces like this:

<image>

then |r_1-r_3|+|c_1-c_3|=|1-2|+|1-1|=1, |1-3|=2, 1<2; and |r_1-r_4|+|c_1-c_4|=|1-2|+|1-2|=2, |1-4|=3, 2<3. It doesn't satisfy the rule.

However, on a 3×3 chessboard, you can place four pieces like this:

<image>

Solution (in JAVA):

Solution:
import java.io.*;
import java.math.*;
import java.security.KeyStore.Entry;
import java.util.*;

public class my {
	private static boolean[] vis;
	private static long[] dist;
	public static void merge(int arr[], int l, int m, int r) 
    { 
        // Find sizes of two subarrays to be merged 
        int n1 = m - l + 1; 
        int n2 = r - m; 
  
        /* Create temp arrays */
        int L[] = new int [n1]; 
        int R[] = new int [n2]; 
  
        /*Copy data to temp arrays*/
        for (int i=0; i<n1; ++i) 
            L[i] = arr[l + i]; 
        for (int j=0; j<n2; ++j) 
            R[j] = arr[m + 1+ j]; 
  
  
        /* Merge the temp arrays */
  
        // Initial indexes of first and second subarrays 
        int i = 0, j = 0; 
  
        // Initial index of merged subarry array 
        int k = l; 
        while (i < n1 && j < n2) 
        { 
            if (L[i] <= R[j]) 
            { 
                arr[k] = L[i]; 
                i++; 
            } 
            else
            { 
                arr[k] = R[j]; 
                j++; 
            } 
            k++; 
        } 
  
        /* Copy remaining elements of L[] if any */
        while (i < n1) 
        { 
            arr[k] = L[i]; 
            i++; 
            k++; 
        } 
  
        /* Copy remaining elements of R[] if any */
        while (j < n2) 
        { 
            arr[k] = R[j]; 
            j++; 
            k++; 
        } 
    } 
	 public static void sort(int arr[], int l, int r) 
	    { 
	        if (l < r) 
	        { 
	            // Find the middle point 
	            int m = (l+r)/2; 
	  
	            // Sort first and second halves 
	            sort(arr, l, m); 
	            sort(arr , m+1, r); 
	  
	            // Merge the sorted halves 
	            merge(arr, l, m, r); 
	        } 
	    } 
	 private static int gcd(int n, int l) {
	        if (l == 0)
	            return n;
	        return gcd(l, n % l);
	    }
//	 public static void dfs(ArrayList<Integer>[] gr,int v,int[] ans,HashMap<Integer,HashMap<Integer,Integer>> map)
//	    {
//	         vis[v]=true;
//	         ArrayList<Integer> arr=gr[v];
//	         for(int i=0;i<arr.size();i++)
//	         {
//	             if(!vis[arr.get(i)])
//	             {  
//	            	 
//	            	 dfs(gr,arr.get(i));
//	             }
//	         }
//	    }
	 private static class Pairs implements Comparable<Pairs>{
	        String v;int i;int j;
	        public Pairs(String a,int b,int c){
	            v=a;
	            i=b;
	            j=c;
	        }
	        @Override
	        public int compareTo(Pairs arg0) {
	            {
	            	if(!this.v.equals(arg0.v))
	            		return this.v.compareTo(arg0.v);
	            	else
	            		return arg0.i-this.i;
	            }
	        }
	    }
	 private static class Pair implements Comparable<Pair>{
	        int v,i;Pair j;
	        public Pair(int a,int b){
	            v=a;
	            i=b;
	        }
	        public Pair(int a,Pair b)
	        {
	            v=a;
	            j=b;
	        }
	        @Override
	        public int compareTo(Pair arg0) {
	            {
	            	return this.v-arg0.v;
	            }
	        }
	    }
	 public static long mmi(long a, long m) 
	    { 
	        long m0 = m; 
	        long y = 0, x = 1; 
	      
	        if (m == 1) 
	          return 0; 
	      
	        while (a > 1) 
	        { 
	            // q is quotient 
	            long q = a / m; 
	            long t = m; 
	      
	            // m is remainder now, process same as 
	            // Euclid's algo 
	            m = a % m; a = t; 
	            t = y; 
	      
	            // Update y and x 
	            y = x - q * y; 
	            x = t; 
	        } 
	      
	        // Make x positive 
	        if (x < 0) 
	           x += m0; 
	      
	        return x; 
	    }
	private static long pow(long a, long b, long c) {
	        if (b == 0)
	            return 1;
	        long p = pow(a, b / 2, c);
	        p = (p * p) % c;
	        return (b % 2 == 0) ? p : (a * p) % c;
	    }
	public static void main(String[] args) throws Exception
	{
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		System.out.println((n/2)+1);
		for(int i=1;i<=n;i++)
		{
			if(i%2==1)
				System.out.println(((i/2)+1)+" "+((i/2)+1));
			else
				System.out.println((i/2)+" "+((i/2)+1));
		}
	}
}